In recent weeks, Mexican authorities had arrested 74 suspects, which included a number of police officers suspected of protecting drug gangs. Wednesday, 73 suspects were officially charged in the killings of 183 people whose bodies were recovered from a number of mass graves found near the U.S.-Mexico border in Tamaulipas, Mexico.

Spokesman for the federal Attorney General’s Office Ricardo Najera said additional suspects are in custody, but he did not know the exact number.

The mass graves were found in the border state of Tamaulipas, and Mexicans were shocked and horrified, which resulted in a number of them filing missing-person reports.

Officials have said that most of the victims were Mexicans migrating to the U.S. who never made it, as they were taken off passenger buses and killed. So far, only 12 victims have been identified. All but one, a Guatemalan man, were Mexican.

It is believed that Los Zetas, a powerful and extremely violent drug gang are behind the mass graves, as they are at war with the Gulf cartel, former allies. When kidnapped, the migrants are often forced to fight for Los Zetas, any refusal to do so results in their demise.

Since April, the Mexican state of Durango has also uncovered a number of mass graves – 226 bodies have been unearthed. The graves and in Durango and Tamaulipas are not thought to be related, and are instead simply the grave-of-choice for Mexico’s drug gangs – Los Zetas in Tamaulipas, and the Sinaloa cartel in Durango.

An anonymous source with the federal police told the Associated Press that the killings in the Sinaloa are a result of a power struggle within the Sinaloa cartel.

Since President Felipe Calderon declared war on the drug world in Mexico in 2006, more than 40,000 people have lost their lives.